Middlesex 144 and 233 for 6 (Simpson 59*) lead Worcestershire 171 (Baker 61*, Murtagh 5-64) by 206 runs
John Simpson led Middlesex's fightback from 39 for 4 with an unbeaten half-century in their LV= Insurance County Championship clash against Worcestershire.
A three-wicket burst by Charlie Morris had put the visitors on top at Lord's, with Middlesex only 12 ahead after teenager Josh Baker's maiden half-century saddled them with a first-innings deficit of 27. Tim Murtagh finished with 5 for 64 as Worcestershire were eventually bowled out for 171.
Max Holden and Martin Andersson both contributed valuable runs before Simpson's unbroken stand of 80 with Luke Hollman steered the Seaxes to 233 for 6 at stumps, an overall advantage of 206.
Looking to wrap up Worcestershire's first innings quickly in the morning, the home side were thwarted by Baker, who bludgeoned a series of boundaries. The 18-year-old heaved Murtagh through midwicket to reach fifty and slammed the bowler's next delivery back past him for four more, eventually finishing unbeaten on 61 from 51 balls.
Murtagh completed his five-for by clean bowling Morris but, by the time last man Dillon Pennington was leg before to Hollman, Worcestershire had added 58 in 45 minutes.
By contrast, Mark Stoneman took the same time to register a duck as he became the first of two victims for Morris before lunch - the other, Stephen Eskinazi, falling to a blinding catch by Gareth Roderick at midwicket.
Morris collected his third straight after the interval when Robbie White edged to second slip and, with Sam Robson caught behind off Joe Leach's outswinger in the next over, Middlesex appeared to be sinking fast.
However, Andersson went for his shots, timing the ball nicely and finding the gaps as he and Holden levered their side out of trouble, sharing a fifth-wicket stand of 66. Ed Barnard broke the partnership by trapping Andersson in front for 45, but Holden looked set for his second half-century of the match as he unfurled some eye-catching strokes, the best of them a hook for four off Pennington.
The left-hander survived a couple of chances but his good fortune ran out at 46, with Daryl Mitchell - who had missed an earlier opportunity to remove Holden - taking a thick edge at second slip.
There was a close call for Simpson on 48 when he hammered Barnard to midwicket but Baker was unable to cling on and the batter took advantage, progressing to 59 not out at the close, with Hollman undefeated on 40.